SETI

I really liked the furious debate that broke out recently among astronomers about whether we should send out signals to the universe saying “we’re here.” It implicitly assumes that somehow, if your science is really advanced, then interstellar travel is possible.

I like it because I hate the idea that the human race will never be able to go beyond this little planetary system “far out in the uncharted backwaters of the unfashionable end of the western spiral arm of the Galaxy,” as Douglas Adams put it in his “Hitch-Hiker’s Guide to the Galaxy.”

We need somebody to do to Einstein’s physics what Einstein did to Newton’s. But while we’re waiting for that, it’s good to know that some quite grown-up scientists (astronomers, not physicists, admittedly, but I’ll take whatever I can get) think it’s worth having a debate about whether we should take the risk of letting all the aliens know we are here.

I missed the debate when it took place at the American Association for the Advancement of Science’s annual conference in San Jose last month because I was on Mars at the time. (Well, somewhere that felt quite like Mars, anyway.) But here’s a couple of quotes to give the flavour of it.

“Any society that could come here and ruin our whole day by incinerating the planet already knows we are here,” said Dr Seth Shostak, Senior Astronomer and Director at the Center for SETI (Search for Extra-Terrestrial Intelligence) Institute in California.

Not so fast, said space scientist and science-fiction writer David Brin. “The arrogance of shouting into the cosmos without any proper risk assessment defies belief. It is a course that would put our grandchildren at risk,” he said. If we send them messages, they may come here and enslave us. Or just eat us.

Now, the traditional way to shut this debate down is to point out that we’ve already been sending out radio and television signals for a hundred years. Therefore, any intergalactic pirates within a hundred light-years of here already know where we are. But it turns out that this isn’t actually true: our radio and television signals begin to fade into the background radio static beyond about one light-year away.

Since the nearest star is more than four light-years away, there’s not much chance that the Klingons or Vogons or whoever you’re worried about knows we’re here yet. (And there goes the plot of “Galaxy Quest”.)

On the other hand, powerful radar signals of the kind that we have been using to map the surface of other planets and moons in our own system travel a very long way, and we’ve already been sending them out for over twenty years. They don’t carry much information – they just say “somebody here can generate microwave radiation” – but just that might be enough to attract unwelcome attention.
This new debate is actually about “active SETI”. We have been doing “passive SETI” – listening for messages from civilisations around other stars – for more than forty years already, using large radio telescopes that can pick up very faint signals. But there are quite strict rules about who should reply if they do get a message.

The First Protocol, drafted by the International Academy of Astronautics SETI Panel in 1989, says that “no transmission in response to a signal or other evidence of extraterrestrial intelligence should be sent until appropriate international consultations have taken place.” But the advocates of “active SETI” want to scrap that and send out an “all call” to the universe.

One of the reasons the debate has got more heated is that we now know planets are as common as dirt. It’s only twenty years since the first confirmed discovery of an “exoplanet”, but now we know of 1,906 of them, mostly orbiting relatively nearby stars and a very small proportion showing Earth-like characteristics. (But the actual number of Earth-like planets may be much higher, since it’s a lot easier to find gas-giants like Jupiter or Saturn.)

There are probably hundreds of thousands of planets in our vicinity (there are 260,000 stars within 250 light-years). If even a mere few thousand of them are Earth-like, then it is imaginable that somebody might come calling in response to the messages we send — if, and only if, it is possible to travel at near- or trans-light speeds.

Nobody knows how light-speed travel could be done, and our current understanding of physics says that it can’t be done. But this would be a very silly debate if scientists were really all convinced that there is no possibility of getting around the current speed limit.

They will never say that it might be possible, because they cannot suggest how it might be done and the risk to their reputations would therefore be extreme. But they are quite happy to engage in a debate that would be totally irrelevant if they didn’t think there is a chance that we – or some other civilisation in our galactic vicinity – will eventually figure out how to do it. And that cheers me up considerably.
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To shorten to 725 words, omit paragraphs 8, 10 and 11. (“Since…Quest”; and “This new…universe”)

“If aliens visit us, the outcome would be much as when Columbus landed in America, which didn’t turn out well for the Native Americans,” said the world’s most famous theoretical physicist, Stephen Hawking, late last month.

He warned scientists not to try to communicate with extra-terrestrials, pointing out that “We only have to look at ourselves to see how intelligent life might develop into something we wouldn’t want to meet.”

Hawking’s concern is shared by others in the field. They don’t object to passive SETI: it can’t do any harm to “Search for Extra-Terrestrial Intelligence” by listening with radio telescopes for the radio emissions of civilizations around other stars. However, they think that active SETI – sending out messages saying “Here we are” – is just asking for trouble.

“Active SETI … is a deliberate attempt to provoke a response by an alien civilization whose capabilities, intentions, and distance are not known to us,” wrote Michael Michaud, former Deputy Director of the Office of International Security Policy in the U.S. State Department, in 2005.

The recent discovery of at least 400 planets orbiting nearby stars makes the issue more urgent, for we now know that planets are very common in our galaxy.

There have already been attempts at active SETI. In 1974 Frank Drake, the astronomer who founded the SETI project, used the Arecibo radio telescope to beam a message towards the globular star cluster M13, which has over a million stars in it.

But M13 is 25,000 light-years away, so we have at least 25,000 years to prepare for any response to the message.

In 2008, however, a high-powered message was sent to the Gliese 581 system, a five-planet system that is only 20 light years away and has two planets in the “habitable zone” for life. The message will get there in 2029.

Several messages have been beamed to other nearby planetary systems since then, in the blithe assumption that anybody there will be friendly. Scientist and author Jared Diamond has said that “those astronomers now preparing again to beam radio signals out to hoped-for extraterrestrials are naive, even dangerous.”

Michael Michaud was equally concerned, warning that “an Active SETI signal … might call us to the attention of a technological civilization that had not known of our existence. We cannot assume that such a civilization would be benign, nor can we assume that interstellar flight is impossible for a species more technologically advanced than our own.”

One assumption embedded in all these warnings is obvious: that life and even intelligence are probably quite common in the universe.

But the other implicit assumption, made even by an outstanding theoretical physicist like Hawking, is that light-speed or faster-than-light travel may be possible.

If it isn’t, then there would be little reason to worry about hostile aliens. They would have no conceivable motive to engage in interstellar raids or conquest, or even interstellar trade, if travel between the stars takes hundreds or thousands of years. Our current knowledge of physics says that faster-than-light travel is impossible, but leading scientists in the field clearly believe that today’s physics may not have the final answers.

We will have to leave that question open for a while, but there are two ways to test the assumption that life is common in the universe.

It will be several decades before we can go to Mars and the moons of Jupiter and Saturn to see if life exists (or once existed) there, but if life really starts up almost anywhere that conditions are suitable, then it’s unlikely that it would have emerged just once here on Earth.

All the familiar forms of life on Earth have the same biochemical make-up, which points to a single, common ancestor.

But the vast majority of species on this planet are microbes, and we have scarcely begun to explore their diversity. Among them there may be species that have a different biochemical basis, perhaps living in isolated parts of the biosphere, or maybe even co-existing with mainstream life.

If we ever found microbes of a different biochemical lineage, we would know that life here has arisen more than once. If so, then it’s probably as common as dirt all across the universe.

If we find no “alien” microbes, on the other hand, we still cannot be sure that life on Earth is unique, for one theory holds that life is spread from planet to planet, and even from star to star, by asteroid collisions. Maybe we only had one collision.

There is another way to test for extra-terrestrial life. As our ability to examine the atmospheres of planets circling other stars improves, we should eventually be able to detect the characteristic changes that abundant life of our kind causes in an atmosphere. Failing to find those changes would not be definitive proof that life is very rare in the universe, but it would be a very strong indication.

In the meantime, maybe it would be wiser not to go looking for trouble. As astronomer Zdenek Kopal said 20 years ago: “Should we ever hear the space-phone ringing, for God’s sake let us not answer, but rather make ourselves as inconspicuous as possible to avoid attracting attention!”__________________________

Gwynne Dyer is a London-based independent journalist whose articles are published in 45 countries.